In prior arts, when an electronic device such as a smart card communicates with a reader-writer, the smart card is connected to a coil of the reader-writer (a POS machine, an NFC phone etc.) via a coil. At the same time, the smart card may be supplied with electricity via the coil of the reader-writer. However, the existing smart card fails to make an effective usage of field energy generated by the reader-writer, which may lead to a waste of electric power of the coil of the reader-writer.